Strain energy shuttle apparatus and method for vibration energy harvesting

Abstract

An apparatus for use in low frequency vibration energy harvesting (VEH) and with actuators requiring a low deflection force. The apparatus includes a piezo flexure that is loaded with a compressive pre-load force to place the piezo flexure under compression. The piezo flexure may be supported at an intermediate point or at one end thereof. The compressive pre-load force produces flexes the piezo flexure into one or the other of two stable positions, these positions being offset on opposite sides of a longitudinal centerline representing the position of the piezo flexure that would be produced without the compressive pre-load force applied thereto. The compressive pre-load effectively provides a negative spring constant which “softens” the piezo flexure and enhances a responsiveness of the piezo flexure to low frequency vibration energy. The piezo flexure also operates over a much wider frequency bandwidth than conventional systems incorporating a tip mass.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of International Patent Application Ser. No. PCT / US / 2004 / 025049 filed Jul. 30, 2004, which in turn claims priority from U.S. Patent Provisional Application No. 60 / 491,122 filed Jul. 30, 2003, the disclosures of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention relates to vibration energy harvesting devices, and more particularly to an apparatus which is ideally suited for harvesting low frequency vibration energy from a vibrating structure. BACKGROUND OF THE INVENTION [0003] Many environments offer a vibration rich environment that is ideal for harvesting vibration energy. Such environments often exist in aircraft and automotive applications where the vibration experienced by an aircraft or automotive vehicle represents energy that could be used to power sensors or other remotely located devices, provided such energy can be harvested by a suitable device. [0004] Vi...

AI Technical Summary

Benefits of technology

[0012] The present invention thus significantly assists in overcoming the inherent structural stiffness of a piezo flexure. The apparatus makes the piezo flexure highly susceptible to very low frequency vibration energy which would otherwise not be sufficient to cause sufficient flexing or bending of the piezo flexure for low frequency vibration energy harvesting applications. A significant advantage of the present invention is that vibration energy harvesting can be accomplished over a significantly wider frequency bandwidth than what is possible with conventional cantilever beam VEH devices using a tip mass.

[0013] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.

Problems solved by technology

When subjected to vibration, the tip of the beam tends to resist motion, thus placing the piezo material under stress.

This stress results in electrical charge accumulation in the piezo material that results in an increase in voltage potential between two points of the material.

However, for this topology to work efficiently, vibration energy must occur at or above the beam resonance frequency.

Additionally, piezo material is usually a ceramic and is fragile when subjected to tension loading which will limit the robustness of the VEH device and its life. FIG. 2 illustrates the relative tip displacement as a function of frequency for this device.

Vibration energy at resonance frequency will provide maximum VEH, but utility is limited by a very narrow bandwidth.

The limitation of needing to “tune” the system around the resonant frequency of the cantilever beam imposes a significant limitation in terms of efficient operation of the system shown in FIG. 1.

The selection of the tip mass, to essentially tune the system to operate efficiently at the resonant beam frequency, means that the system will not be efficient in harvesting energy at other frequencies above and below the resonant frequency of the cantilever beam.

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